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Egg, ovum or female reproductive body of multicellular animals, particularly the complex structure produced by birds, reptiles, and certain mammals that matures outside the body of the parent. For a discussion of egg production as human food, Poultry Farming.From the anatomical point of view, eggs consist of a minute speck of protoplasm, the germ, tread, or cicatricle, from which the animal develops, and a much larger amount of food material, the yolk. In addition, all eggs have some form of protective coating, either a jelly mass, a shell, or a covering membrane.
The structure and development of eggs of different species vary with the condition under which the egg is produced and matures. Animals that deposit their eggs to hatch outside the body are described as oviparous; those that produce eggs with soft coverings that mature within the body are called viviparous; and those that produce hard- or tough-shelled eggs that mature within the parent's body are said to be ovoviviparous. An egg that contains little yolk is either retained and nourished by the mother, or, if deposited outside the body, develops quickly into a self-sustaining form such as larva. The number of eggs produced varies with the likelihood of their survival. When conditions militate against the survival of eggs, as in the case of fish eggs, a large quantity of eggs is produced as many as 14 million by the turbot. The number of individuals that can develop from a single egg varies from one to several hundred in certain chalcid flies.
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